1. Field of the Invention
The present invention relates to a manufacturing method of a planar resistance heating element wherein an aluminum foil deposited on an insulating substrate is etched in a desired pattern, carbon paste is printed and then current input terminals are connected in parallel, and to a planar resistance heating element made using the manufacturing method. More particularly, the present invention relates to a manufacturing method of a planar resistance heating element wherein an aluminum foil acting as an electrode layer deposited on an insulating substrate is tempered in multiple steps to prevent heat deformation and a resistor element is formed using carbon paste made of a mixture of thermally conductive carbon, graphite, a resin, a solvent and a hardener, and to a planar resistance heating element made using the manufacturing method.
2. Description of the Prior Art
A planar resistance heating element is a heater which uses far infrared rays radiated from an insulated planar radiator heated by conduction heat generated from a resistance heating element embedded in the radiator. The resistance heating element may be made of metallic thin plates, surface treated metallic oxides, ceramic plates, carbon black, or carbon fibers.
Among conventional planar resistance heating elements, one heating element that does not have a positive temperature coefficient (PTC) resistor element generates heat using direct current, has low resistance and conducts a large amount of electric current, thereby complicating temperature control. Another heating element having electric current directly applied thereto without separate electrodes has non-uniform electric conductivity. In yet another heating element comprising electrodes and a resistor element, the electrodes are formed through mixing powder of a metal such as silver with a resin and printing the metallic mixture, the resistor element is formed through mixing a carbon-based material with a resin and printing the carbon mixture, and electric current is then applied to the resistor element to generate heat. Although silver is an excellent electric conductor, it is silver paste made of a mixture of a synthetic resin and silver powder that is used in a planar resistance heating element, resulting in poor electric conductivity. Further, a complex and expensive manufacturing process is needed.
To solve these problems, the inventor of the present invention has developed a manufacturing method of a planar resistance heating element (Korean Patent No. 411401), which comprises the steps of: printing an etch-resist in a desired pattern on an aluminum foil deposited on an insulating substrate; spraying an etchant on the aluminum foil to cause a portion of the aluminum foil, where the etch-resist is not printed, to corrode away; cleaning the etch-resist and etchant using an alkaline solution; printing in a desired pattern using carbon paste; and connecting current input terminals in parallel to an electrode layer of the aluminum foil.
However, there are some unsolved problems in the manufacture of a planar resistance heating element. A polyethylene terephthalate (PET) film, which is typically used as an insulating substrate, may be deformed owing to heat, causing irregular printing in a manufacturing process or non-uniform heat conduction after the manufacturing process. Additionally, in the manufacture of the carbon paste acting as a resistor element, an improper composition ratio between electrically conductive carbon, a resin, a solvent and a hardener in the carbon paste may deteriorate physical properties including heat-generating properties.